The application entails studies of the transcriptional regulation and function of neuropeptide transmitters in the Drosophila nervous system. During the previous funding period it was found that in a subset of dFMRFergic neurons, this peptide is upregulated after a 5h delay by the LIM domain gene apterous. Genetic screens are proposed to isolate factors downstream of apterous. A yeast two-hybrid screen is proposed to identify homeodomain transcription factors that regulate dFMRFa in another neuronal type, OL2. In aim 2, the expression patterns of two enzymes involved in neuropeptide amidation, dPHM and dPAL, will be analyzed. Aim 3 focuses on the regulation of these amidation enzymes. Promoter constructs will be made to identify the minimal sequences driving lacZ in the normal pattern. Promoter constructs will be used in the background of apterous mutations to investigate whether this gene also drives the amidation enzymes in the same sets of neurons that express dFMRFa. Another gene identified in the previous granting period, dimmed, will be characterized genetically and molecularly in aim 4. In dimmed mutant embryos, the dFMRFa expression is globally decreased without concomitant morphological abnormalities. Aim 5 is a collaborative effort between the investigator and Drs. Hall and Meinertzhagen to investigate the function of dFMRFa in the OL2 neurons that have been implicated in circadian rhythmicity.